1. Field of the Invention
The present invention also relates to the provision of a system, preferably electrically powered, for providing forward thrust for a fluid immersed boring tool. More particularly, the invention provides the necessary thrust, a dynamic force, for the operation of a rotary boring tool in situations, such as the drilling of generally horizontal bore holes, where the force of gravity does not act to provide effective forward thrust. The invention is especially efficaceous with flexible drill pipe or conduit such as may be used in drilling bore holes having a small radius of curvature.
2. Description of the Prior Art
Hydraulic power has been used to rotate boring tools in drilling vertical and deviating bore holes for many years. Typical of such tools is the Dyna-Drill, offered by the Dyna-Drill Company, a division of Smith International, Inc. of Irvine, Calif. The power generated by the Dyna-Drill is used, and only used, to rotate the drilling bit. The system is used with conventional drill pipe and drill collars to provide the desired weight on bit or thrust.
A. McDougall, U.S. Pat. No. 469,841 discloses a system for dredging in which a boring tool is mounted on the same shaft as a propeller. Flow of liquid circulated for the dredging operation causes both to rotate. Thrust for the boring tool, however, is obtained by the weight of the system. The reverse circulation system disclosed actually tends to lift McDougall's boring tool rather than to advance it.
A water jet propelled nozzle head for cleaning pipes and conduits is disclosed by U.S. Pat. No. 2,710,980 to Pletcher in which jets direct water against vanes to rotate an outer section relative to an inner section which is fixedly secured to a hose. Neither the rotative nor the advancing force developed is adequate for subsurface earth boring.
More generally, the prior art is rich in the field of drilling directionally deviated wells using rotary bits turned either from the surface or by subsurface mud turbines.
Roy Cross in U.S. Pat. No. 2,251,916 discloses a system for solution mining of salts occurring in thin layers where forced circulation of the solvent is necessary to effectively contact and dissolve the material to be mined. Generally, he discloses the use of horizontally directed nozzles to direct a stream of fresh solvent, specifically water, against the face of the material to be mined, specifically potash salts. In one form of his invention, shown in his FIG. 5, Cross schematically shows an electrically driven device which purportedly will produce horizontal circulation and at the same time cut away residue salts not dissolved by the solvent. Rotation of an electric motor shaft is supposed to rotate a drill bit on one end thereof and a propeller generating forward thrust on the other end. Since the motor housing is freely suspended and has no resistance to twisting, as soon as any torque is imposed on the shaft by the propeller or the drill bit, the housing rather than the shaft would rotate. Thus, the device shown is inoperative.